1. Field of the Invention
The present invention relates to a getter which can physically and chemically absorb gas and a method of manufacturing the getter, and particularly to a getter which can maintain its performance for a long time even under an atmosphere in which getter performance is easily deteriorated and to a method of manufacturing the getter.
The present invention also relates to an airtight chamber which maintains a pressure that is equal to or less than an atmospheric pressure and to an image forming apparatus having the getter. Particularly, the image forming apparatus of the present invention is preferably used in the image forming apparatus which comprises: a vacuum chamber, an electron source; and an image-forming member for forming an image by irradiation of an electron beam emitted from the electron source.
2. Related Background Art
A substance which can physically and chemically absorb residual gases present in vacuo or in the atmosphere of inert gases or the like is usually referred to as the getter.
Preferable material used as the getter is a material having a high residual gas absorption rate, and being able to keep the absorption rate slow in order to keep the vacuum as long as possible in a system in which the material is disposed and to eliminate the influence of the residual gases in the atmosphere of inert gases or the like.
As the getter material, metal simple bodies of Ba, Li, Al, Zr, Ti, Hf, Nb, Ta, Th, Mo, V, and the like or alloys formed of the metal simple bodies are heretofore known.
Moreover, the getter for heating and evaporating the metal simple bodies or the alloy of the metal simple bodies in vacuo or in the atmosphere of inert gases or the like, and exposing a clean metal surface to chemically absorb a residual gases component in vacuo is called an evaporating getter, while a getter for the heating in vacuo or in the atmosphere of inert gases or the like to diffuse inwardly an oxide coat present on the surface, and exposing the metal surface to the top surface at every heating to absorb the residual gases in vacuo is called a non-evaporable getter.
The non-evaporable getter is formed of the metal simple body mainly containing zirconium (Zr), or titanium (Ti), or the alloy containing these metals, and a getter ability is usually obtained and used by forming a film of the metal or the alloy on a substrate of stainless, nichrome, or the like, and heating the substrate by energization heating and other means. For example, the manufacture method comprises: placing about 100 xcexcm of a material powder to the substrate of stainless, nichrome, and the like by a rolling process, and the like; and calcining the substrate at a temperature of about 1000xc2x0 C. in vacuo. This is performed in order to take a large reactive surface area by using the powder and effectively perform physical and chemical absorption.
In order to obtain the getter performance of the non-evaporable getter manufactured as described above, the vacuum, inert gases, and other atmospheres are used as the atmosphere in which the getter is disposed, and an active surface is formed and prepared for gas absorption by applying the heating operation (activation operation) to decompose and diffuse the surface oxide.
However, when the thin film of the metal simple body of Zr, Ti, and the like is formed on the substrate of stainless, nichrome, and the like by generally known means such as a vacuum evaporation process, a very stable oxide is formed on the surface of the formed film simultaneously with atmospheric exposure, and the heating to a high temperature of 800 to 900xc2x0 C. in vacuo is necessary for removing the oxide film by diffusion to form the active surface (Japan J. Appl. Phys. Suppl. 2, Pt. 1, 49, 1974). Additionally, since after the activation operation the reaction of the simple body metal thin film and the residual gases in vacuo occurs usually at 200xc2x0 C. or a higher temperature, the getter performance is hardly fulfilled around the room temperature.
Therefore, the non-evaporable getter can perform the activation operation at a lower temperature, and the getter material enables the getter function to be obtained at or near room temperature after the activation operation has been developed.
For example, the getter material of an alloy of 84 wt % of Zr-16 wt % of Al, disclosed in Japanese Patent Publication No. 46-39811, is a powder of a crushed alloy block obtained by melting Zr and Al (tradename: St-101, SAES Co. in Italy). When the Zrxe2x80x94Al alloy powder is used instead of the simple-body Zr powder, the surface oxide film can be diffused/removed at a low temperature, the particles can therefore be prevented from being sintered with one another, and a surface structure in which the surface area is relatively maintained is constructed. Moreover, the Zrxe2x80x94Al alloy is higher in safety than Zr which is highly reactive in the room-temperature atmosphere. It is disclosed that the weight ratio having a highest absorptivity is set to be Zr 84%-Al 16{circumflex over ( )} in SAES Co. by changing the weight ratio of Zrxe2x80x94Al in a range of Al 6 to 37% to prepare the alloy on trial and by comparing the getter characteristics (Proc. 4th Int. Symp. on Residual Gases in Electron Tubes 221, 1972). However, the alloy does not have a high residual gases absorption rate, and has a problem that it takes much time to exhaust a large amount of gas at room temperature. To obtain a sufficient absorption rate from this alloy, the residual gases has to be absorbed by heating the activated alloy to 300xc2x0 C. or a higher temperature.
Moreover, from the standpoint of prevention of reduction of the surface area by sintering the mixture of different types of powders, as disclosed in Japanese Patent Publication No. 53-1141, the getter material is obtained by mixing the simple-body metal powder of Zr, Ta, Hf, Nb, Ti, Th, U, and the like with the Zrxe2x80x94Al alloy powder, but the material has a disadvantage that a sufficient exhaust ability cannot be recognized in the room temperature.
Furthermore, U.S. Pat. No. 3,584,253 discloses a getter obtained by mixing Zr simple-body powder and graphite powder.
In this example, the alloy powder mixed with Zr powder has no getter ability or insufficient ability if any, and the main point is to sinter the powders with each other not to reduce the surface area. Therefore, since the alloy powder is added, the getter ability is deteriorated. If the alloy powder to mix is provided with the getter ability, the reduction of the surface area can be prevented, so that the deterioration of the getter ability can be avoided.
As the non-evaporable getter, as disclosed in U.S. Pat. No. 4,312,669, the non-evaporable getter material consisting of a three-element alloy of Zr, V, Fe, or Zr, Ni, Fe has been developed. The non-evaporable getter is obtained by mixing the Zr powder with the Zrxe2x80x94Vxe2x80x94Fe alloy powder having the getter ability, or the Zrxe2x80x94Nixe2x80x94Fe alloy powder so as to prevent the sintering of the powders. Additionally, the getter function is obtained even when activation occurs at a temperature lower than a conventional temperature because of the high reactivity (absorptivity) of the Zrxe2x80x94Vxe2x80x94Fe alloy, or the Zrxe2x80x94Nixe2x80x94Fe alloy.
However, in view of the material cost, it is unfavorable to use the alloy powder which causes many synthesis problems and which is difficult to form into powder. Moreover, it is troublesome and unfavorable to fix the mixed powder onto the base material by the rolling process or the like, sinter the materials in vacuo and further bond the materials. Moreover, since the getter function is obtained in the low temperature around the room temperature after the activation, the getter easily reacts, that is, the getter is quickly deteriorated. There is a disadvantage that desired characteristics cannot be maintained for a long time dependent on a use environment. For example, the member with the getter disposed thereon is subjected to a process in which a high temperature has to be obtained in a low vacuum atmosphere containing oxygen, moisture, and the like, and in this supposed situation, the desired characteristics cannot necessarily be maintained as occasion demands.
An image forming apparatus using the above-described getter will next be described.
In an apparatus in which a phosphor as an image-forming member is irradiated with the electron beam emitted from the electron source, and the phosphor is allowed to emit light to display an image, the inside of a vacuum chamber enveloping the electron source and the image-forming member has to be held in a high vacuum. When gas is generated inside the vacuum chamber, and pressure rises, influences differ with gas types, but the electron source is adversely affected, thereby lowering the electron emission amount, so that bright image display cannot be performed. Moreover, the generated gas is ionized by the electron beam to form an ion, accelerated by an electric field for accelerating the electron, and collides against the electron source to damage the electron source in some cases. Furthermore, electric discharge is caused inside, and the apparatus may be destroyed in certain cases.
The vacuum chamber of the image display is usually formed by combining glass members and bonding a combined part by a fritted glass, and the like. Once the bonding is completed, the pressure is maintained by the getter installed in the vacuum chamber.
As the material used as the getter, the material having a high absorption rate of the residual gases in vacuo and being able to keep the absorption rate long is preferable in order to keep the vacuum as long as possible in the system in which the getter is disposed.
As the getter, in a usual CRT, a deposition film is formed on a chamber inner wall by energizing or heating by a high frequency the alloy mainly containing Ba in the completely bonded vacuum chamber, and the gas generated inside is absorbed by the film to maintain a high vacuum. The getter like this Ba, which is evaporated by heating in vacuo to absorb the residual gases in vacuo with a clean metal surface, is usually referred to as the evaporating getter.
With respect to the usual CRT, at present, a plane type display has been advanced in development utilizing the electron source in which a large number of electron-emitters are disposed on a plane substrate. In this case, the volume of the vacuum chamber is reduced as compared with the CRT, but the area of the wall surface which generates the gases does not decrease. Therefore, when the gas is generated to the same degree as in the CRT, the pressure in the chamber largely rises, thereby exerting a serious influence onto the electron source.
Since the CRT has a characteristic shape, there is a sufficient wall surface part provided with neither electron source nor image-forming members such as the phosphors inside the vacuum chamber, and the above-described evaporating getter material can be deposited on the part. In the plane type display, however, most of the area of the vacuum chamber inner surface is occupied by the electron source and the image-forming member. When the above-described evaporating type getter film adheres to this part, adverse influences such as wiring short are generated. Therefore, a place where the getter film can be formed is limited to a place in which neither electron source nor image-forming member is disposed. Moreover, when the size of the plane type display increases to some degree, it is difficult to secure a sufficient area of the getter deposition film as compared with the gas emission amount.
To solve this problem, and to secure a sufficient getter deposition film area, in the plane type display, there are proposed: a method, as shown in FIG. 25A, comprising extending a wire getter outside an image display region between the phosphor and the electric field emitting device disposed opposite to each other in an envelope, that is, on an outer peripheral part, and depositing and forming the getter film on the wall surface of the outer peripheral part (Japanese Patent Application Laid-Open No. 5-151916); a method, as shown in FIG. 25B, comprising attaching a getter chamber having a getter material for forming a getter film to the side of the space between a face plate and a rear plate (Japanese Patent Application Laid-Open No. 4-289640); a method comprising forming a space between an electron source substrate and the rear plate of the vacuum chamber, and forming the getter film in the space (Japanese Patent Application Laid-Open No. 1-235152); and the like.
The problems of the gas generation inside the vacuum chamber in the flat panel display include the above-described problem, and a problem that the pressure easily rises locally. In the image display having the electron source and the image-forming member, inside the vacuum chamber, the gas is generated mainly in the image display region irradiated with the electron beam, and in the electron source itself.
In the conventional CRT, since the image-forming member is apart from the electron source, and between both the getter deposition film is formed on the inner wall of the vacuum chamber, the gas generated in the image display member is broadly diffused to reach the electron source, a part of the gas is absorbed by the getter film, and the pressure fails to rise excessively in the electron source. Moreover, since the getter film is also formed around the electron source itself, the excessive local pressure rise is not caused even by the gas emitted from the electron source itself.
In the flat panel display, however, since the image display member is close to the electron source, the gas generated from the image display member reaches the electron source before it is sufficiently diffused, thereby causing the local pressure rise. Particularly, in the middle part of the image display region, the gas cannot be diffused to the region with the getter film formed thereon, and it is therefore considered that the local pressure rise is remarkable as compared with the peripheral part. The generated gas is ionized by the electron emitted from the electron source, and accelerated by the electric field formed between the electron source and the image display member to damage the electron source or cause the electric charge, so that the electron source is destroyed in certain cases.
In view of this situation, in the flat panel display having a specific structure, the getter material is disposed in the image display region, and the gas generated in the image display region is immediately absorbed in the disclosed constitution.
For example, according to Japanese Patent Application Laid-Open No. 4-12436, in the electron source having a gate electrode for extracting the electron beam, a method of forming the gate electrode with the getter material is disclosed, and an electric-field emitting cathode using a conical protrusion as a cathode, and a semiconductor electron source having pn junction are illustrated.
Moreover, according to Japanese Patent Application Laid-Open No. 63-181248, in the plane type display with a structure in which an electrode (grid), and the like for controlling the electron beam are disposed between a cathode group and the vacuum chamber face plate, a method of forming the film of the getter material on the controlling electrode is disclosed.
Furthermore, U.S. Pat. No. 5,453,659 discloses that a getter member is formed in a gap between striped phosphors on the image display member (anode plate). In this example, the getter material is electrically separated from the phosphor and a conductor electrically connected to the phosphor, and the getter is activated by applying an appropriate potential to the getter to radiate/heat the electron emitted from the electron source, or by performing the energization heating of the getter.
Additionally, the plane type display having a simple structure and manufacture method is needless to say preferable from the standpoint of a production technique, manufacture cost, and the like. When the process of manufacturing the electron-emitter constituting the electron source is constituted of a thin film lamination and a simple processing, or when the large-size electron source is manufactured, the manufacture by the techniques, requiring no vacuum apparatus, such as a printing process is demanded.
In this respect, for the electron source disclosed in the Japanese Patent Application Laid-Open No. 4-12436 and having the gate electrode constituted of the getter material, the manufacture of the conical cathode chip, or the manufacture of the bonded semiconductor requires an intricate process in the vacuum apparatus, and the size enlargement is limited by the manufacture apparatus.
Moreover, in the apparatus in which the control electrode, and the like are disposed between the electron source and the face plate as disclosed in the Japanese Patent Application Laid-Open No. 63-181248, the structure is complicated, and the intricate processes such as the positioning of the members are required in the manufacture process.
Furthermore, in the method of forming the getter material on the anode plate as disclosed in the U.S. Pat. No. 5,453,659, the electric insulation needs to be taken between the getter material and the phosphor, and the getter material is formed by repeatedly performing patterning by a photolithography technique for a precise fine processing. Therefore, the process becomes intricate, and the size of the image display which can be manufactured is limited by the size of the apparatus for use in the photolithography.
With respect to the image displays, examples of the electron-emitter constituting the plane type display which can satisfy the above-described requirement of the easy manufacture process include a transverse electric field emitting device, and a surface conduction electron-emitter. The transverse electric field emitting type electron-emitter is formed by disposing the cathode having a protruded electron-emitting part on the plane substrate opposite to an anode (gate) for applying a high electric field to the cathode, and can be manufactured by thin film deposition processes such as deposition, sputtering, and plating, and the ordinary photolithography technique. Moreover, in the surface conduction electron-emitter, the electron is emitted by passing a current to the electroconductive thin film having a high resistance part, and one example is disclosed in Japanese Patent Application Laid-Open No. 7-235255 by the present applicant et al.
Since the electron source using the above emitters is not provided with the gate electrode shaped as disclosed in the Japanese Patent Application Laid-Open No. 4-12436, or the control electrode disclosed in the Japanese Patent Application Laid-Open No. 63-181248, the getter cannot be disposed in the image display region with the means similar to the disclosed means, and the getter is heretofore disposed outside the image display region. As described above, however, the gas generated in the image display region cannot efficiently be absorbed in the plane type display.
To solve the problem, Japanese Patent Application Laid-Open No. 9-82245 discloses that the getter is disposed in the image display region of the image display using the surface conduction electron-emitter. However, since a new wiring is necessary for activating the getter, the manufacture process becomes intricate. Since the getter is disposed in the vicinity of the electron-emitter, the electric conduction with the wiring or the electrode is feared. Additionally, since the evaporating Ba getter used as the getter on the wiring is formed by heating and evaporating the material stored in a container, the container is left after the evaporation, and the positioning of the Ba getter is necessary.
An object of the present invention is to realize a getter which has preferable characteristics.
One invention of the getter according to the present application is constituted as follows.
There is provided a getter which comprises a getter layer on a base surface containing at least one of Zr and Ti.
Here, the getter layer preferably contains at least a non-evaporable getter material, or the getter layer preferably contains at least Ti. Moreover, in the getter layer the evaporated materials are preferably deposited. Evaporating means include the heating of a material, and a sputtering process using a physical energy. Specifically, an electron beam deposition process, a jet printing process, and a sputtering process can be used. Additionally, here the jet printing process is a method of evaporating the material, conveying the material together with a conveying gas, and applying the material to an applied part.
Moreover, one invention of the getter according to the present application is constituted as follows.
There is provided a getter which comprises a getter layer on a base surface containing a non-evaporable getter material.
Here, the getter material on the base surface preferably contains at least one of Zr and Ti, and the getter layer preferably contains at least Ti.
In the above-described inventions, the base surface preferably has an undulation.
Moreover, in the above-described inventions, the base surface is preferably porous.
Furthermore, in the above-described invention, the base surface has an undulation, and the thickness of the getter layer is preferably smaller than the roughness of the undulation of the base surface.
Additionally, in the above-described inventions, the base surface is preferably formed by spray-coating a base surface composition.
Moreover, in the above-described inventions, the base surface is preferably formed by fixing a base surface composition powder to a base component by a adhesive material. Particularly, the adhesive material is preferably a hardened material by the bonding of a silicon atom and an oxygen atom, or the adhesive material is preferably formed by solidifying a liquid or gel adhesive. For example, concretely, the base surface is preferably obtained by mixing the adhesive with the powder containing at least the getter material to form a paste material, applying the material onto the base component, and calcining. The adhesive preferable for use is prepared by dissolving a ladder-like silicone-based oligomer in an organic solvent.
Moreover, the present application includes the invention of an airtight chamber which holds the inside to an atmospheric pressure or a lower pressure, and which comprises inside the getter according to any one of the above-described inventions.
Furthermore, the present application includes the invention of an image forming apparatus in which an electron source and an image-forming member for forming an image by irradiation of an electron from the electron source are disposed in an envelope holding the inside to an atmospheric pressure or a lower pressure,
the image forming apparatus comprising: the getter according to any one of the above-described inventions in the envelope.
Here, the electron source may include a plurality of electron-emitters. A cold cathode device is preferably used as the electron-emitter. Particularly, a surface conduction electron-emitter is preferable.
Moreover, here, the invention of the above-described image forming apparatus can particularly preferably be applied to a constitution in which the electron source and the image-forming member substantially constitute planes, and are disposed opposite to each other.
Furthermore, the present application includes the following invention as the invention of a method of manufacturing the getter.
The method of manufacturing the getter comprises: a step of forming a base surface containing at least one of Zr and Ti; and
a step of forming a getter layer on the base surface.
Additionally, the present application includes the following invention as the invention of the method of manufacturing the getter.
The method of manufacturing the getter comprises: a step of forming a base surface containing at least non-evaporable getter materials; and
a step of forming a getter layer on the base surface.
In each invention of the method of manufacturing the getter, the base surface is preferably exposed to an atmosphere containing a substance to be absorbed by the base surface before the step of forming the getter layer on the base surface. This is because the substance absorbed by the base surface acts during the formation of the getter layer on the base surface and the state of the getter layer is set to be appropriate for the absorption. Particularly, the step of forming the getter layer on the base surface may comprise a step of evaporating and depositing the material to form the getter layer. Additionally, the exposure of the base surface to the atmosphere containing the substance to be absorbed by the base surface is preferably achieved, for example, by the exposure to the atmospheric air. Moreover, the exposure step is not limited to the step performed after the base surface is formed. The base surface may be formed in the atmosphere containing the substance to be absorbed.
Additionally, the airtight chamber of the present invention can be used as the envelope of image forming apparatuses such as a display using the electron-emitter, a plasma display, and a fluorescent display tube, or as the envelope of a vacuum tube. In the display using the electron-emitter, the fluorescent display tube, or the vacuum tube, the inside of the airtight chamber (envelope) is set to provide a high vacuum so that the emitted electron can reach the image-forming members such as phosphors, or the anode. The plasma display is different in that an electric discharge gas such as Ne, and Xe having the atmospheric pressure or a lower pressure is sealed, but is common in that the getter is used for absorbing an impurity gas in the chamber, so that the getter of the present invention is preferably used.
The image forming apparatus of the present invention can, as described above, take a form in which the image forming member is irradiated with an electron emitted from the electron-emitter in response to an input signal to form an image. Particularly, the image display in which the image-forming member is a phosphor can be constituted.
The electron-emitter can be provided with a passive matrix arrangement in which a plurality of cold cathode emitters are matrix-wired by a plurality of row-directional wirings and a plurality of column-directional wirings. Moreover, there can be provided a ladder-like arrangement in which a plurality of rows of cold cathode emitters are arranged by connecting opposite ends of a plurality of cold cathode emitters arranged in parallel (referred to as the row direction), and electrons from the cold cathode emitters are controlled by a control electrode (referred to also as the grid) arranged above the cold cathode emitters along a direction (referred to as the column direction) crossing at right angles to the row-directional wiring.
Furthermore, according to the idea of the present invention, the invention is not limited to the image display, and can also be used as a light-emitting source which is a substitute for a light-emitting diode of an optical printer constituted of a photosensitive drum, a light-emitting diode, and the like. Moreover, in this case, the invention can also be applied not only as the linear light-emitting source but also as a two-dimensional light-emitting source by appropriately selecting the above-described m row-directional wirings and n column-directional wirings. In this case, the image-forming member is not limited to the phosphor used in the following embodiment and other substances which directly emit light, and a member in which a latent image is formed by charging the electrons can also be used.
Moreover, according to the idea of the present invention, the present invention can also be applied, for example, to an electron microscope, in which the member to be irradiated with the electron emitted from the electron source is other than the image-forming members such as the phosphor. Therefore, the present invention can also take a form as a general electron beam apparatus in which the member to be irradiated is not specified.